#include <iostream>
using namespace std;
class Square;

class Rectangle {
		int width, height;
	public:
		int area() {
			return (width * height);
		}
		void convert(Square a);
};

class Square {
		friend class Rectangle;
	private:
		int side;
	public:
		Square(int a): side(a) {}
};

void Rectangle::convert(Square a) {
	width = a.side;
	height = a.side;
}

int main() {
	Rectangle rect;
	Square sqr (4);
	rect.convert(sqr);
	cout << rect.area();
	return 0;
}